This invention relates to a merchandise, vehicle, or personnel tagging technique for the purpose of selective detection or identification when carried or passed through the system.
The problem of theft (shoplifting) is a serious economical problem for almost all categories of business, including retail stores, manufacturing facilities, etc. There is an increasingly serious problem world industry-wide involving the pilferage of manufactured items from storage facilities, such as, warehouse and department stores, industrial plants, military installations, by service personel, employees, customers, visitors and incidental parties.
One approach has been to tag each item of merchandise and then use various techniques to detect the tagged item when it is being stolen. Most prior methods of pilferage control and prevention are too expensive to be used on a large scale-particularly the tags are too large and/or expensive. A number of different tag implementations are already in use which variously employ packaged resonant radio antennas, non-linear diode/antennas, permanent magnets. There are certain weaknesses associated with each approach; for example, the relative ease with which to shield the electromagnetically illuminated tags either with a person's body in the microwave systems or with small amounts of normally carried metal in the radio frequency implementations. The permanent magnet tag systems on the other hand are susceptible to false alarms from remanent magnetism in steel arch supports in shoes and nearby similar magnetized moving bodies.
U.S. Pat. No. 3,836,842 is a method whereby locations, typically outside locations, are marked by a passing marking device placed therewith. The marking device is responsive in a damped oscillatory manner when radiated by at least one pulse of magnetic energy, i.e., an induction field. An interrogating instrument is the source of the induction field. After an induction field has been generated, the interrogating instrument monitors the frequency range within which the marking device is resonantly responsive. When a response is detected the interrogating instrument provides an indication of the response. The marking device is particularly useful for marking locations which are buried or are from time to time concealed. With a portable interrogating instrument, an operator, traversing the general area of a location, is thus able find the location without the aid of a visible stake or other similar fixture.
The marking device of U.S. Pat. No. 3,836,842 can be an encapsulated passive resonant electrical circuit of an elongated cylindrical shape. A coil of insulated conductor wire placed on a ferrite magnetically soft elongated core forms the inductive portion of a tank circuit. A capacitor connected in parallel with the coil completes the tank circuit. Ideally, an almost infinite Q circuit is stated to be desirable and thus the coil and the capacitor must be of reasonably low resistance and loss, respectively. Likewise the core must be of a low loss material. It is also stated to be desirable that the resonant frequency be stable with respect to wide temperature variations. Since the coil and core inherently have positive temperature coefficients the capacitor is preferably of the polystyrene type having a negative temperature coefficient. Thus the marking device is at least partially temperature-compensated.
The tag system of the patent is not commercially viable for pilferage control, detection and prevention as large quantities of inexpensive tags are needed to achieve that objective.